1. Field of the Invention
The present invention relates to an open-close cover assembly of an image forming apparatus.
2. Description of the Related Art
There is known an image forming apparatus (e.g., a printer) in which an image is formed on a roll sheet, an image-formed portion of the roll sheet is cut into an image-formed sheet, and the image-formed sheet is discharged upwardly.
Such image forming apparatus has a sheet discharge unit provided with an open-close cover that is opened for use as a sheet tray on which image-formed sheets can be placed upright and stacked. It should be noted that in a case where image-formed sheets of large quantity are discharged and stacked on the open-close cover, a cover open angle must be accurately maintained for smooth sheet discharge and stacking operations.
If the open-close cover which is in an open state is applied with an excessive force acting in a direction to open the cover, the cover can be damaged and/or a cover mounting part of a main unit of the image forming apparatus can be damaged.
Accordingly, a cover open-close mechanism has been proposed (Japanese Patent Publication No. 4449761) that has a cover provided at its both ends with a pair of hinge bases on which protrusions are formed so as to be fitted into holes that are formed in a pair of hinge receiving portions provided in an apparatus main unit, thereby rotatably mounting the cover to the apparatus main unit. One of the hinge receiving portions is formed with a rotation prevention part that prevents the cover from rotating. When the cover is applied with an excessive force acting in a cover opening direction, one side of the cover in which the rotation prevention part is not provided is largely opened. As a result, the cover is twisted and detached from the apparatus main body, thereby preventing the cover and/or the apparatus main body from being damaged.
However, when an excessive force is applied to another side of the cover in which the rotation prevention part is provided, the cover is hardly detached from the apparatus main unit. This causes a fear that the cover and/or the apparatus main unit can be damaged. In addition, the strength for withstanding a force acting in a cover opening direction is not sufficient since the rotation prevention part is only provided on one side of the cover. Accordingly, when image-formed sheets of large quantity are stacked on the cover, the cover is inclined rearwardly and the open angle of the cover becomes large, thereby sometimes preventing smooth sheet discharge.
A sheet feed tractor has also been proposed (Japanese Examined Patent Application Publication No. H06-088702 and corresponding U.S. Pat. No. 5,127,568), in which a pair of hinge pins are provided in a lid and fitted into grooves formed in a pair of hinges provided in a frame to thereby openably and closeably mount the lid to the frame, and in which one of the hinges has an extension formed by an elastically deformable stopper. When the lid is applied with an excessive force acting in a lid opening direction, the stopper of the frame is elastically deformed, so that the lid is detached from the stopper and prevented from being damaged.
However, if a user does not restore the lid detached from the stopper to an original position and if the lid is subsequently applied with an excessive force acting in the lid opening direction, the lid can be damaged.